The problem of degassing a liquid prior to some processing operation is well known, particularly in clinical procedures, scientific determinations, industrial processes and artificial organs. In a dialysis machine, for example, contained gases within a liquid, typically tap water, may have to be reduced to approximately 1 ppm or less, in order for dialysis functions to be properly effected. The gas (air) that is present in the tap water is present either as entrained gas (micro- or macro-bubbles) or dissolved gas. A liquid can contain an amount of gas, under equilibrium conditions, that is limited by both temperature and pressure. The lower the temperature and the higher the pressure the greater the amount of dissolved gas. In theory, therefore, simply increasing the temperature while reducing the pressure to suitable levels and allowing equilibrium to be reached would enable suitable degasification of the liquid. However, typical processes involve much shorter residence times than are available to achieve equilibrium.
It is known in the prior art to desgasify by inducing turbulence sufficient to create cavitation in the liquid, while maintaining a hard vacuum or at least a negative pressure within the volume in which the liquid is confined. Most of the known processes and machines are, however, batch-type systems, because significant difficulties are encountered in continuous degasifying to a low gas concentration level. It is extremely difficult, for example, to insure that the output effluent is constantly and uniformly degassed to below 1 ppm, and it is further difficult to provide positive fluid flow when working against a hard vacuum. Cost and reliability considerations prevent practical usage of an extended series of stages, pumps and interconnection controls.
Among the various techniques that have been used in the prior art to reduce the time required to reach equilibrium under given temperature and pressure conditions, it is of course known to use a combination of temperature and pressure reduction greatly in excess of that needed for a given degasification level, so that there need not be a full wait for equilibrium. However, this technique is not suitable for achieving low gas concentrations and is based upon use of an over-design, which inherently involves higher costs. It is also known to reduce the diffusion distance for the gas within a liquid, by increasing the surface area-to-volume relationship of the liquid, as by creating a falling sheet or film of liquid or the cavitation technique previously mentioned. These approaches have heretofore been limited in throughput, and have required costly or delicate equipment. A variation of this technique involves insertion of an abundance of nucleation sites, such as sharp elements, which reduce the diffusion distance of the gas through the liquid. Considering all of these techniques, however, it still has not heretofore been feasible to provide a continuously operating, relatively low cost and highly reliable degasifier capable of achieving low gas concentration levels in the liquid.